1. Field of the Invention
This invention relates to a process and to an electrolytic cell for the production of fluorine.
2. Discussion of Prior Art
The designs of presently used fluorine-producing electrolytic cells give rise to many problems. These problems include:
1. Poor Energy Efficiency
This is due to two main factors:
(a) a high anode overvoltage due to the formation of a resistive carbon fluoride polymer film at the anode surface, and
(b) a high electrolyte ohmic loss, due to the necessity (in present designs) of allowing a large gap between anode and cathode to minimise the recombination of the product fluorine and hydrogen which would otherwise reduce the current efficiency.
2. Low Space/Time Yield
This can be defined as the mass of product per unit volume of electrolytic cell, per unit time. In present designs of cells, the space/time yield for fluorine is inherently low due to the poor ratio of unscreened anode area to cell volume. The thickness of the anodes (&gt;30 mm), and the large anode and cathode gap mentioned above compound the problem. The end result is that an electrolytic plant for the production of modest quantities of fluorine occupies a vast area (compared with analogues such as chlorine).
3. Poor Reliability
Anode failures are well known to those "skilled in the art", such failures including: "polarization" (the development of an unusually high anode overvoltage), anode breakage, failure of the electrical connections, and burning in fluorine.
4. Low Pressure of Product Gases
It is an inherent feature of the fluorine-producing electrolytic cells presently used that for safe operation the fluorine off-gas pressure can be no greater than the hydrostatic head provided by the submerged gas separating skirts when the evolved hydrogen off-gas pressure is at atmospheric pressure. In practice, this effectively limits the evolved fluorine pressure to a maximum of approximately 10 cm water gauge. Operation above this pressure is theoretically possible if the hydrogen and fluorine pressures are kept in perfect balance, but a sudden failure of an external seal or joint could then result in a fluorine/hydrogen explosion within the electrolytic cell.
5. Maintenance and Corrosion Problems
There are also maintenance problems with present designs caused, to some extent, by the highly corrosive nature of fluorine, and the effect of "misting" in which an aerosol of the electrolyte becomes entrained in the fluorine gas and is deposited on the walls of pipework outside the cell, thus leading to restrictions and eventually to blockages in the pipework.
It is, therefore, an object of the present invention to provide a process and an electrolytic cell for the production of fluorine in which the above-mentioned problems are alleviated to some extent.